Human amniotic membrane derived from the placenta has been used for nearly 100 years as a transplantable biomaterial for the surgical reconstruction of various tissues in the human body. Such a membrane has been utilized widely in the management of ocular surface disorders; utilized as a biological dressing or graft for skin (burns, skin wounds, skin ulcers); utilized to prevent tissue adhesion in surgical procedures of the spine, abdomen and pelvis; utilized as a wrap for tendon and nerve repair procedures; and utilized as a graft for dental/oral procedures. Normally, such a membrane has is either dehydrated or cryopreserved prior to storage until ready for surgical transplantation.
The placental tissue, from which the amniotic membrane is derived, is harvested after birth or after elective Cesarean section surgery. At full term of gestation, the fetal membranes of the placenta are comprised of two principal layers: (1) the outer chorion layer which is in contact with maternal cells and forms the outer aspect of the sac, and (2) the inner amniotic membrane layer which contains large amounts of collagen and is bathed by amniotic fluid contained within the sac. The amniotic membrane is a thin, translucent, elastic tissue which forms the innermost layer of the amniotic sac and the placenta. Histologically, the amniotic membrane is comprised of 3 layers (FIG. 2): an epithelial monolayer, a basement membrane and stroma. The stroma can be further subdivided into a compact layer, a fibroblast layer containing a loose network of fibroblasts, and a spongy layer.
There are storage challenges with the amniotic membrane in the cryopreserved forms as this requires refrigeration or freezing to maintain these tissue grafts. The dried forms of the amniotic membrane has a storage advantage however, the methods of drying/dehydration involve the use of heat, chemicals and sometimes the removal of the epithelial layer which renders an altered histologic profile and contributes to the destruction or reduction of the naturally occurring biological properties of the amniotic membrane as seen in nature. Described herein are amniotic membranes which are dehydrated via a lyophilized (freeze dried) method without using heat or chemicals to hereby better preserve the naturally occurring biological properties of the amniotic membrane seen in nature. Such grafts, when properly prepared, can be stored at ambient temperatures for prolonged periods of time until ready for transplantation while maintaining the histologic and biological properties seen in utero.
Amnion membrane as a tissue graft provides a natural biological barrier, a matrix for cell migration and proliferation, and naturally occurring growth factors and other biological components that contribute to healing at the site of transplantation. Such a membrane when transplanted has the added benefit of the absence of immune rejection due to the lack of most of the major histocompatibility (HLA) antigens and viable cells.